The purpose of the proposed studies is to use in vivo microscopic techniques to systematically analyze of the physiological control of lymphatics (50-150 mum in diameter) are viewed through an intravital videomicroscope and intralymphatic pressure (P) and diameter (D) are continuously monitored. The lymphatic contractile cycle is then modelled after the cardiac cycle; i.e., basic cardiac function parameters (e.g., contractile frequency, stroke volume, ejection fraction) are used to analyze the flow generating capabilities of the lymph "Hearts". Lymphatic muscle mechanics are analyzed by monitoring the rate of smooth muscle shortening (dD/dt), the rate of pressure development (dP/dt), tension development and force of contraction (i.e., contractility). The proposed studies will address 6 specific aims: 1) test the hypothesis that the initiation of lymphatic contraction is totally dependent upon the degree of smooth muscle stretch (i.e., myogenic) and independent of nervous activity; 2) study the length-tension relationship for lymphatic smooth muscle; 3) determine the inotropic and chronotropic effects of the sympathetic and parasympathetic nervous systems on mesenteric lymphatics; 4) evaluate the ability of collecting lymphatics to respond to functional increases in lymph production caused by glucose-coupled intestinal fluid absorption; 5) characterize the response of the mesenteric lymphatic pump to increases in lymph flow that follow lipid ingestion and determine if this response is dependent on the type of lipid absorbed (e.g., short, medium or long chain fatty acids) and 6) determine if gastrointestinal peptides released in response to intraluminal lipid augment lymphatic contractile activity. The results of these studies will provide a firm basis for future studies on gastrointestinal lymphatics and the propulsion of lymph by the mesenteric lymph hearts.